In recent years, low heat build-up of tires for automobiles has been highly demanded from the perspective of enhancing the fuel economy of such automobiles.
In response to such demands for low heat build-up, it has been known that use of a polymer with small hysteresis loss (e.g. natural rubber, and high-cis butadiene rubber) as a rubber composition for tire treads is effective to achieve low heat build-up (reduce rolling resistance).
On the other hand, it has been also known that a problem exist in that processability is poor when a polymer with small hysteresis loss is used.
Regarding such required characteristics and problems, for example, Patent Document 1 describes “a conjugated diene rubber composition containing a conjugated diene rubber (A) which is obtained by emulsion polymerization and which has a compounded proportion of an aromatic vinyl monomer unit of 30 to 50 wt. %, and a modified conjugated diene rubber (B) which is obtained by solution polymerization and which has a hydroxy group, a compounded ratio of the conjugated diene rubber (A) to the modified conjugated diene rubber (B) being from 55:45 to 85:15 in terms of weight ratio of “conjugated diene rubber (A):modified conjugated diene rubber (B)”” (Claim 1) and also describes a tire containing a crosslinked product of this rubber composition (Claims 4 and 5).